As is known, the traditional paper making machines are provided with one or more bands (commonly known as felts) circulating along closed annular paths, by means of which the paper being formed is transported and processed.
Each section of the machine has, in general, a specific type of band.
To obtain good quality paper, it is important to assess the conditions of the band in each section, in addition to monitoring the conditions of the material transported on it.
The conditions of the band, in terms of absorption of water, transport of water and permeability to water, affect the quality of the paper sheet, in particular during the pressing phase. It is therefore important to monitor the conditions of the band, in particular during the pressing phases of the paper sheet.
It is known that the conditions of a band operating on a paper making machine are assessed by means of apparatus which simultaneously measures permeability and humidity of the band, as illustrated for example in U.S. Pat. No. 7,506,550. The apparatus described in U.S. Pat. No. 7,506,550 includes permeability and humidity measurement devices, installed directly on the paper making machine, in a predetermined position along the band and connected to a processing and control unit for continuous monitoring of the band. Another apparatus for controlling the conditions of a band is disclosed in WO2010/035112.
Said apparatus, however, detects data that cannot be inter-correlated for the purpose of making a reliable diagnosis of the condition of the circulating band. An inaccurate and unreliable diagnosis of the condition of the band inevitably results in losses for the paper making machine, in terms of both quality and energy saving.